1. Field of the Invention
The present invention relates to a seal device between a fastening bolt and bolthole in a gas turbine disc, and more specifically to a seal device for sealing a gap between a fastening bolt and bolthole in a disc of a steam-cooled type gas turbine so as to reduce leakage of cooling medium to the outside.
2. Description of the Prior Art
In the present state of gas turbine cooling systems, air-cooled systems are the trend. Air is partially extracted from a compressor to be introduced into a stationary blade, a moving blade and a rotor for cooling thereof, and the air, after being used for cooling, is discharged into a combustion gas passage. Recently, along with a high efficiency power plant, a combined cycle plant is being developed in which a gas turbine and a steam turbine are used in combination, and a steam cooled system of a gas turbine is in the process of development to be used in the combined cycle plant. The steam-cooled system is such that steam is partially extracted from the steam turbine to be introduced into the stationary blade, the moving blade and the rotor of the gas turbine for cooling thereof. The steam, after being used for the cooling, is recovered to the steam turbine side for effective use thereof.
FIG. 6 is a cross sectional view showing one example of a steam-cooled type gas turbine in the prior art where such a steam-cooled system as mentioned above is employed and cooling of moving blades by steam is carried out, similar to the present invention. In FIG. 6, numerals 21, 22, 23 and 24 designate first to fourth stage moving blades, respectively, and numerals 51, 52, 53 and 54 designate first to fourth stage stationary blades, respectively. Numeral 31 designates a disc on a rotor side and numeral 32 designates a bolthole, which is provided in plural pieces along the circumferential direction in the disc 31 so as to pass through a disc portion in the axial direction, the disc portion carrying the moving blades 21 to 24 of the respective stages. Numeral 33 designates a fastening bolt which is inserted so as to pass through the bolthole 32 in the axial direction and to fixedly fasten the disc portion carrying the moving blades of the respective stages. Numeral 34 designates a steam introduction passage, into which steam of an appropriate temperature, extracted from the steam turbine side, is introduced via a disc end portion. Numeral 35 designates a steam recovery passage for recovering therethrough the steam after it has been used for the cooling of moving blades. The steam recovery passage 35 is provided so as to be deviated in phase from the steam introduction passage 34 in the circumferential direction. Numerals 36, 37, respectively, designate cavities of the disc 31.
The gas turbine of FIG. 6 is an example which employs a steam-cooled system for the first stage moving blade 21 and the second stage moving blade 22 and an air-cooled system for the third stage moving blade 23 and the fourth stage moving blade 24, as there is less thermal load and thus less advantage for a steam-cooled system in the latter two stages as compared with the former two stages. In FIG. 6, the extracted steam is fed into the disc 31 end portion to be supplied therefrom into the steam introduction passage 34. Steam 41 so supplied enters the cavity 36 and then, passing through a steam passage (not shown), enters the second stage moving blade 22 to cool the blade 22 while passing through an introduction side of a cooling steam passage provided in the blade 22. The steam, after being used for cooling, passes through a recovery side of the cooling steam passage to be recovered into the cavity 37. Likewise, the steam 41 enters the first stage moving blade 21 to cool the blade 21 and, after being used for the cooling, is recovered into the cavity 37.
The steam recovered after having cooled the first stage moving blade 21 and the second stage moving blade 22 gathers in the cavity 37 and then, passing through the steam recovery passage 35, is recovered from the disc 31 end portion as recovery steam 42 of an elevated temperature. It is returned to the steam turbine side for effective use thereof.
FIG. 7 is a cross sectional view taken on line X--X in arrow direction of FIG. 6. FIG. 7 shows a state where the rotor is rotating. The fastening bolt 33, inserted into the bolthole 32, has a diameter which is slightly smaller than that of the bolthole 32. With the rotor being rotated as shown there, the fastening bolt 33 is biased outwardly due to the centrifugal force, so that a gap S occurs on an inner side within the bolthole 32. A portion of the steam from the cavity 36 or 37 passes through the gap S and leaks into a low pressure part 38, as shown by numeral 43 in FIG. 6. If the amount of the leakage becomes large, a loss of recovery steam occurs so as to lower the efficiency.
As mentioned above, in the prior art gas turbine which uses air as a cooling medium, the stationary blade, moving blade and rotor are cooled by air, and the air, after having been used for cooling, is discharged into the combustion gas passage with no recovery thereof being necessitated. In the gas turbine which employs the steam-cooled system, however, the steam, after being used for cooling, is recovered to be returned to the steam turbine side, so that the temperature-elevated steam, through cooling, is used effectively. Therefore, if the steam leaks outside, it results in a loss of thermal energy by that degree, leading to a lowering of efficiency. In the prior art gas turbine, if the bolt is biased in the bolthole due to centrifugal force, a gap deformation occurs between the bolt and the bolthole. A problem in this case is that a ring-shaped seal component that is widely used in the prior art for sealing a gap of concentric circular shape cannot be used.